A Study to Learn About Salanersen's (BIIB115) Effects on Movement and Its Safety in Participants Aged 15 to 60 Years With Spinal Muscular Atrophy (SMA) Who Are Either New to SMA Treatment or Were Previously Treated With Risdiplam

The primary objective of the SOLAR study is to evaluate the clinical efficacy of salanersen in participants with SMA who are treatment-naïve or previously treated with risdiplam. The secondary objective of the study is to evaluate the safety, tolerability, and pharmacokinetics (PK) of salanersen.